Control circuit for an implantable heart-assist pump of the back-pressure balloon type

ABSTRACT

The pump (10) has variable volume means (24) co-operating with a distinct volume (20) through which the blood flows for the purpose of varying said volume (20) through which the blood flows in cyclical and controlled manner. According to the invention, the control circuit for the pump comprises: means for sensing data representative of aortic pressure (P(t)); means for sensing data representative of venous oxygen concentration (PO 2V ); means for sensing data representative of aortic oxygen concentration (PO 2A ); means for sensing data representative of heartbeat frequency (F); and/or means for sensing data representative of the myocardial contractility (dP/dt). The circuit can control the rates (u(t), v(t)) at which said volume varies during the systolic and diastolic phases of the myocardium, and also the instants (t A  ; t R ) at which said variation of the volume starts during the systolic and diastolic phases.

The invention relates to a control circuit for an implantableheart-assist pump of the back-pressure balloon type. The technique usingan intra-aortic back-pressure balloon is well known for providingeffective hemodynamic assistance to the left ventricle in the event ofcongestive heart failure: the balloon is inserted in the down branch ofthe aorta and is inflated during the diastolic phase of the heart cycle,and as a result injects an additional volume of blood into the networkof arteries both upstream and downstream from its position. Deflatedduring the following heart systole, it decreases the load on the leftventricle thus enabling blood flow rate to be increased. The hemodynamicbalance is positive: an increase in the injection fraction; a decreasein the telediastolic pressure. Thus, the balloon delivers additionalenergy which the ventricle is not able to supply, and the state of thepatient is very significantly improved.

Implanted systems have already been proposed which make it possible toimplement that technique in an entirely self-contained manner, forexample as described in U.S. Pat. No. 5,222,980, or indeed in Frenchapplication 96/00949 filed on Jan. 26, 1996 belonging to the sameproprietor as the present application and entitled Pompe d'assistancecardiaque implantable du type a ballonnet de contrepression [Animplantable heart-assist pump of the back-pressure balloon type].

Both of those documents describe a permanent implantable heart-assistpump inserted in the descending aorta, operating on the above-mentionedprinciple of a back-pressure balloon constituted by a flexible andelastic membrane in the form of a sleeve whose axis coincides with thatof the aorta and which is put in the place of a segment of aorta thathas been removed. The membrane is contained in a rigid chamber havingsubstantially the same shape as the membrane at rest, and into which ahydraulic fluid is injected from an external generator, therebycompressing the membrane and thus reducing the volume of blood that itcontains. Conversely, extracting the hydraulic fluid causes the insidevolume of the membrane to increase, and thus the pump to be filled.

More precisely, an object of the present invention is to provide acontrol circuit for such an implantable heart-assist pump which controlsthe appliance so that its behaviour is as physiological as possible,i.e. it mitigates the heart failure without requiring excessive orantinatural effort from the weakened myocardium, and which, throughoutthe cardiovascular system, generates blood flow having characteristics,in particular pressure wave, that are as close to possible to those of ahealthy organism.

Another object of the invention is to provide variable control of thepump that is adapted to the real hemodynamic demand of the patient,firstly to limit he energy consumption of the implanted appliance, andsecondly, and above all, to disturb the natural hemeostatic equilibriumas little as possible, thus avoiding possible organic complications inthe long term following implantation of the pump.

To this end, the invention provides a circuit for controlling animplantable heart-assist pump of the back-pressure balloon type of theabove-specified type, i.e. comprising variable volume means co-operatingwith a separate volume through which blood flows for the purpose ofmodifying said volume through which blood flows cyclically and incontrolled manner, the circuit being characterized in that it includesat least some of the means in the group comprising: means for sensingdata representative of aortic pressure; means for sensing datarepresentative of venous oxygen concentration; means for sensing datarepresentative of aortic oxygen concentration; means for sensing datarepresentative of heartbeat frequency; and means for sensing datarepresentative of the myocardial contractility.

According to a certain number of advantageous characteristics:

the circuit includes heart-assist control means for controlling thevariable volume means, said control means including at least some of themeans in the group comprising: means for controlling the rate ofvariation of said volume during the systolic phase of the myocardium;means for controlling the rate of variation of said volume during thediastolic phase of the myocardium; means for controlling the instant atwhich said volume variation starts during the systolic phase; and meansfor controlling the instant at which said volume variation starts duringthe diastolic phase;

in a first embodiment, the assistance given to the heart may bepredetermined, operating on the basis of: (i) a programmed set of restvalues for reference parameters, said parameters comprising at least oneof the following parameters: the rate at which the volume varies duringthe systolic phase of the myocardium; the rate at which the volumevaries during the diastolic phase of the myocardium; the instant atwhich said volume variation during the systolic phase begins; and theinstant at which said volume variation during the diastolic phasebeings; and (ii) an algorithm for correcting at least one of saidparameters as a function of the heartbeat frequency;

the circuit further includes means for sensing data representative ofthe metabolic needs and/or the physical activity of the patient; and

in a second embodiment, the assistance given to the heart may beautomatic, operating on the basis of: (i) a sensed representative dataset generated in real time comprising at least: aortic pressure; venousoxygen concentration; aortic oxygen concentration; heartbeat frequency;and myocardial contractility; (ii) a corresponding set of referenceparameters; (iii) differences determined between said representativedata set and said reference set; and (iv) an algorithm for implementingvariable volume means as a function of the differences determined inthis way. In which case, advantageously, the algorithm for implementingvariable volume means serves to track heart assistance, particularly byapplying the assistance by successive approximations; in addition, theheart assistance may serve to correct the data set generated in realtime or the reference set.

Other characteristics of the invention appear on reading the followingdescription of an embodiment of the invention.

FIG. 1 is a diagrammatic view showing the pump of the invention, itscontrol circuit, and the environment in which the appliance as a wholeis implanted.

FIG. 2 shows how operation of the FIG. 1 pump is modelled.

FIG. 3 shows the characteristic of the pressure wave as a function oftime over one heart cycle, with and without assistance by the pump ofthe invention.

In FIG. 1, there is shown an implantable heart-assist pump of a typethat is itself known (e.g. from above-mentioned U.S. Pat. No. 5,222,980or from French application 96/00949), in which the main element 10comprises a rigid body 12, typically in the form of a circular cylinder,open at both ends and inserted in the descending aorta 14, the axis ofthe aorta and the axis of the body 12 coinciding, and with both of thesetwo elements having substantially the same diameter.

The rigid body 12 contains a flexible membrane 16. In the embodimentshown, the membrane 16 at rest is similar in shape to the body 12, so asto be substantially a close fit therein, and it is secured thereto atboth ends over its entire periphery.

Between the body 12 and the membrane 16, there is thus defined a closedintermediate space 18 of variable volume, and inside the membrane 16there is defined a central space 20, also of variable volume, with thisvolume decreasing when the volume 18 is increased, and vice versa.

The volume of the space 18 is increased by injecting a hydraulic fluid(typically a biocompatible aqueous saline solution, e.g. a physiologicalserum) via one or preferably more points connected via a duct 22 to avariable pressure source 24 controlled by control electronics 26.Advantageously, a hydraulic fluid reservoir 28 may also be provided inthe form of a septum that is accessible percutaneously by means of ahypodermic needle to enable the volume and/or the salinity of the fluidto be adjusted, or to enable it to be emptied out.

The invention relates more particularly to the circuit 26 which controlsthe pressure source 24.

As shown in FIG. 2, the pump can be modelled in the form of a piston 25whose displacement in one direction or the other gives rise to a changein the volume 20 of the aorta. This artificial variation of the volume20 in the aorta 14 is comparable to the natural dilatation of a healthyartery as the result of the elasticity of the walls of the artery, andis of greater amplitude.

More precisely, during heart systole, contraction of the myocardium 29causes, in succession: the pressure to rise in the left ventricle 30;the aortic valve 32 to open; and blood to be ejected into the aorta 14.Heart beats are such that systole is of perceptibly shorter durationthan the heart cycle, thereby increasing the speed of systolic ejection.The elasticity of the arteries avoids the need for a correspondingexcess demand for power from the ventricle to overcome the load providedby the inertia and the resistance of the column of blood that it is toput into motion, and thus makes it possible, so to speak, to deliverenergy at a lower instantaneous rate during diastole.

Heart failure is characterized by the incapacity of the ventricle todeliver the quantity of blood required by the organism because it doesnot have the necessary power, and this may or may not be accompanied byhardening of the arteries (although hardening of the arteries aggravatesthis pathological condition very greatly).

Under such circumstances, the heart-assist pump performs two functions:firstly it provides additional elasticity in artificial manner to theaorta, as described above, giving the same benefit as that provided bythe natural elasticity of the arterial network; secondly, and inaccordance with an original aspect of the invention, the pump candelivery additional energy to the circulation system during diastole.

Considering the model shown in FIG. 2, the total volume producedartificially by displacing the piston 25 in the heart-assist pump at theend of displacement is given by: ##EQU1## where Σ is the surface area ofthe piston and u(t) is the speed of displacement of the piston whichvaries as a function of time throughout all or part of systole S.

This volume of blood which is stored in the pump during systole issubsequently reinjected into the aorta during the diastole D followingthe systole, by the piston moving in the opposite direction at speedv(t), which is likewise variable as a function of time during all orpart of diastole D (where the speed v(t) is independent of u(t)).

From an energy point of view, during systole the pump takes energy E_(i): ##EQU2## P(t) being the pressure exerted by the blood on the piston.

During diastole, the pump restores energy E_(o) : ##EQU3##

The energy balance E_(o) -E_(i) due to the prosthesis can be:

negative, which means that the heart is delivering energy to theprosthesis (this possibility is clearly not advantageous);

zero or slightly positive: the pump then behaves essentially asadditional elastance (elasticity factor), that combines with the naturalelastance of the artery in the operating scheme described above andproviding the same benefit. Under such circumstances, the heart providesall of the energy that is required. This can apply, for example, to apatient who is resting; and

positive, in which case the assistance given to the heart is takenfurther, the substantial increase in the volume of blood stored by thepump and the corresponding decrease in the systolic pressure making itpossible significantly to increase the systolic ejection volume usingenergy from the heart that is less than or equal to that which itprovided before the increase. In addition to its function of providingadditional elastance, the pump acts during diastole to provide the extraenergy required to compensate for the heart deficit.

In this way, by modulating the volume stored and the energy delivered bythe pump, it is possible to deliver assistance to the heart on acycle-by-cycle basis in "doses" as a function of the hemodynamic demand.The doctor can organize this "dosage" so as to load the heart to themaximum of its operating capacity under all circumstances, or to only afraction thereof, by means of adjustments and of automatic responses asdescribed below.

The major advantage of proportional dosage of this type is to minimizethe energy consumption of the appliance.

It is also possible to limit the action of the machine on thecirculation system so as to disturb the natural homeostatic equilibriumas little as possible, thereby avoiding severe repercussions in the longterm on major organic functions, such as the renal and hepaticfunctions.

Finally, it can be expected that this method of providing assistancethat is adaptive and limited encourages rehabilitation of the heart.

Such heart assistance is implemented by the circuit of the inventionwhich operates as follows.

DATA

Firstly, the state of the cardiovascular system is characterized by datawhich is made accessible to the appliance by sensors. The data used isas follows:

aortic pressure as a function of time P(t);

venous oxygen concentration PO_(2V) ;

aortic oxygen concentration PO_(2A) ;

heartbeat frequency F; and

myocardial contractility dP/dt.

This list not limiting, thus, minute volume MV and/or posture and/orstill further parameters can also be taken into account from appropriatecorresponding sensors (e.g. from accelerometers for posture and activityG).

DATA ACQUISITION

The data is obtained as follows:

P(t): by a specific sensor disposed in the pump on its blood side or itshydraulic fluid side.

PO_(2V) and PO_(2A) : by specific sensors, one (34) placed in the rightheart (PO_(2V)), or else in the veins, and the other (36) in the aortaflow passing through the pump (PO_(2A)). The desired parameter isPO_(2A) -PO_(2V). The system could be made to operate on the basis ofusing PO_(2V) only, but that would reduce its performance.

F: by means of an electrocardiogram (ECG) or directly from thesubstitute frequency synthesizer, where appropriate. The ECG is pickedup by a ventricular endocavity electrode 38 in the right heart. Itdefines the instant at which the right ventricle is depolarized fromwhich it is possible to deduce the instant at which the left ventricleis depolarized, and the heartbeat frequency F. In a variant, the ECG canbe picked up by an epicardiac electrode placed on the left ventricle.

dP/dt: this parameter is the mean slope of the pressure in the leftventricle during its isovolumetric contraction, which slope is obtainedfrom the pressure difference and the duration between the beginning ofdepolarization and the opening of the aortic valve, as detected by thecorresponding discontinuity in P(t).

Depending on the use that is to be made of it, data is deduced, aftervalidation, from the measurements performed:

a) during the preceding heart cycle in order to track quickly or toestimate a trend; or

b) on the basis of a sliding weighted mean over a determined number ofpreceding cycles, so as to perform smoothing and/or allow effects tostabilize.

The aortic pressure P(t) is sampled at predetermined intervals.

The data varies as a function of state parameters such as physical,gastrointestinal, or cerebral activity, posture, the environment, or theresult of coexisting pathologies, drug levels, etc. The data is also tosome extend interdependent.

EXPRESSION OF THE NEED OF THE HEART FOR ASSISTANCE

The need of the heart for assistance is determined from a set of dataand combinations of reference data. This data set is established takingaccount of the cardiovascular pathology and is input into the applianceby programming.

The reference set has its own dynamics as a function of the stateparameters: for example, the expression for normality when providing aneffort is represented by the values for P(t), PO_(2A) -PO_(2V), anddP/dt which are different from the values that represent normality atrest. The same applies to normality with varying levels ofpharmaceuticals, etc.

The reference set must therefore be programmed at two levels:

one relating to reference data at rest; and

another relating to algorithms for correcting the preceding data as afunction of variations that are the result of daily activity. In thisrespect, the main factor giving rise to variation is physical activity,so the algorithms can generally be limited to representing physicalactivity by way of heartbeat frequency.

Finally, the reference data set is determined by two-variable data:P(t,F), PO_(2A) (F)-PO_(2V) (F), F, dP/dt(F) and/or combinations ofthese data items.

In the event of a change in pharmaceutical levels or in pathologicalstate, both levels of the programming should be modified accordingly.

Once programming has been performed, the differences observed in dailylife relative to the reference values, once they have exceeded a certainthreshold, determine the heart's need for assistance. For example, whenproviding an effort, any increase in PO_(2A) -PO_(2V), or any drop inPO_(2V), will trigger heart assistance which was not previously requiredwhile at rest, or which was required but to a lesser extent.

HEART ASSISTANCE

The way in which assistance is provided is defined by programming as afunction of the nature, the amplitude, and the rate at which thedifferences vary.

As soon as assistance is provided, a tracking program is launched inaddition to the above, e.g. including a higher rate of sampling,starting algorithms, tracking algorithms, terminating algorithms, etc.,acting on the way in which assistance is delivered as a function of theway in which the disturbance causing it varies and as a function of theway in which the response of the organism varies.

WAYS IN WHICH ASSISTANCE IS GIVEN TO THE HEART

The assistance to be given to the heart is determined by pistondisplacement speeds u(t) during systole and v(t) during diastole, whichcorrespond respectively to the volumes Σ·u(t) and Σ·v(t) that arerespectively accumulated by and restored by the pump, and on the time oforigin for said functions relative to the heart cycle, t_(A) for u(t)and t_(R) for v(t).

Determining u(t) and t_(A)

As explained above, the artificial increase in the aortic volume Σ·u(t)gives rise to an increase in the systolic flow rate which hasrepercussions on the energy delivered by the left ventricle and on theenergy efficiency thereof. The effects are as beneficial as those ofsoftening the arteries. It is also important for u(t) and t_(A) to beproperly matched to heart function.

For example, a preferred form of the profile for u(t) may decreaseexponentially, by analogy with the elastic behavior of the arteries,while t_(A) can control the beginning of systole by anticipation so asto reduce systolic pressure.

In practice, t_(A) and the profile of u(t) are adjusted as a function ofthe patient by programming and they do not vary as a function of patientactivity. The amplitude of u(t), and consequently of ∫_(s) u(t)dtconstitutes the essential action parameter for giving assistance to theheart by artificially increasing aortic volume, or in other words, bydecreasing postcharge on the left ventricle.

The amplitude of u(t), and in particular the corresponding quantity∫_(s) u(t)dt for the total volume stored by the pump Σ·∫_(s) u(t)dt, isdetermined as a function of the desired heart flow rate. Given theresponse time of the cardiovascular system to the impulse appliedthereto, the amplitude u(t) can be incremented progressively, with eachincrement being defined as a function of the result of the precedingincrement within a given time period, and is limited by the capacity ofthe heart and of the prosthesis to respond.

Determining v(t) and t_(R)

Reinjection is governed by the profile of v(t) and by t_(R), with theamplitude of v(t) being dependent on the amplitude of u(t) since ∫_(s)u(t)dt=∫_(D) v(t)dt, given that the piston returns to the same positionafter performing one cycle.

On the basis of arterial pressure at the beginning of diastole and inco-operation with arterial compliance, v(t) and t_(R) determine theinstantaneous arterial pressure and arterial flow rate during diastole.At equilibrium, total arterial flow rate during diastole, plus thearterial flow rate during systole, is naturally equal to the flow ratethrough the left ventricle.

When the state of the patient is stable, applying assistance to theheart associated with determined values of u(t), t_(A), v(t), t_(R) thusgives rise to a disturbance followed by a spontaneous re-equilibrium ofthe cardiovascular system to achieve a new operating regime defined bythe heart flow rate, the various ventricular and aortic, systolic anddiastolic pressures, and consequently the amounts of energy delivered bythe heart and by the prosthesis.

It will be understood that:

although giving assistance to the heart improves the cardiovascularstate, the exact effects thereof are not known until after the state hasstabilized, when it can be found by reading all of the data;

assistance should preferably be applied to the heart by successiveapproximations; and

assistance can be given to the heart at different degrees of intensitydepending on the amount by which postcharge is to be diminished and onthe energy supplied by the prosthesis.

PROGRAMMING PROTOCOL

Heart assistance can be either predetermined or else automatic.

Predetermined assistance is obtained by programming u(t), t_(A), v(t),t_(R) at rest and by the algorithm for correcting u(t) and the profileof v(t) and also t_(R) as a function of the heartbeat frequency F.

Automatic assistance is obtained by programming the reference set, thecorrection algorithms for said set as a function of the stateparameters, which, in practice, reduce to the heartbeat frequency F, thethreshold for triggering assistance, and the intensity thereof.

Programming comprises the following operations:

A. For predetermined assistance:

1. Implementing sensors; reading results.

2. Programming assistance: u(t), t_(A), v(t), t_(R).

3. Programming algorithms for correcting u(t), the profile of v(t), andt_(R) as a function of heartbeat frequency.

B. For automatic assistance:

1. Implementing sensors; reading results.

2. Programming the reference set and the correction algorithms.

3. Programming implementation of assistance as a function of differences(threshold and intensity) relative to the reference set.

OPERATION

The programmed appliance performs the following operations:

1. Reading the sensors, and generating the data set in real time.

2. Correcting the reference set in real time (automatic assistance).

3. Determining the differences between the data set (1) and thereference set (2) (automatic assistance).

4. Triggering assistance as a function of the differences (automaticassistance) or correcting assistance as a function of the heartbeatfrequency (predetermined assistance).

5. Triggering the tracking program. Protocol for successiveapproximations (automatic assistance).

6. Holter registration of the data and of significant events, ofoperating parameters, in particular energy consumption.

7. Recording statistical data.

It will be observed that the appliance can equally well correct thereference set (operation 2) or the data set in real time (inversecorrection).

A COMPARATIVE EXAMPLE FOR THE RESULTING PRESSURE WAVE

FIG. 3 shows the shape of the pressure wave, i.e. the function P(t), foraortic pressure as a function of time.

Pressure is given in millimeters of mercury, which is the non-SI unit inwhich blood pressures are universally expressed in practice (1mmHg=133.322 Pa).

The solid line curve shows aortic pressure without ventricularassistance, while the dashed line curve shows the same pressure withventricular assistance, with reinjection (reduction of the variablevolume 20) taking place between t=200 ms (end of systole) and t=340 ms.

Initially considering the curve for pressure without giving assistanceto the heart, at equilibrium the pressure at the end of diastole isequal to the pressure at the beginning of systole, with the cycle beingstabilized and repetitive.

The area defined by the curve of P(t) from t=0 to t=750 ms (one fullcycle at a rate of 80 heart beats per minute) and the horizontal axis(going down to P=20 mmHg which is the end-of-diastole pressure of theleft ventricle) is representative of the total capillary flow rate,equal to the total flow rate of the heart:

    Q.sub.cardiac =area(P)/R=1/R ∫.sub.0.sup.750 P(t)dt

where R is the resistance of the arterial-venous capillaries, which isincluded in the relationship Q_(c) =P/R giving the capillary flow rate.

With reference now to the curve for assistance being given to the heart(dashed line curve), various observations can be made.

Firstly, although reinjection takes place in the example shown at thebeginning of diastole, it could equally well begin a little before theend of systole, providing it always comes to an end at t=340 ms. Afterthe end of reinjection, the aorta, which has been dilatated by thereinjection, begins to discharge in approximately exponential mannerinto the downstream arterial network. As a result, the diastolicpressure at the end of diastole is greater than said pressure at the endof the preceding diastole. At the moment that assistance is put intooperation, the cycle will therefore not be in equilibrium, and it willreturn to equilibrium a few cycles later.

Secondly, it can be observed that the difference between the solid linecurve and the dashed line curve is representative of the difference incapillary flow rate with and without assistance.

With assistance, the capillary flow rate is lower during systole andgreater during diastole. The balance (the difference between the areadefined by the curves before and after the instant of reinjection)represents the contribution due to assisting the heart flow rate. Theexact gain in heart flow rate can be determined after the pressureprofile has stabilized, so as to take account of the fact that puttingassistance into operation changes several physiological magnitudes suchas diastolic and systolic pressure, filling of the left ventricle,energy of the right ventricle, resistance R (which decreases), frequencyF (which decreases), etc. in particular with improved irrigation of thecoronaries. Stabilization on a new equilibrium state will therefore nottake place immediately.

It can also be observed that the heart flow rate, as represented by thearea defined by the curve during the duration of a cycle, is deliveredvia the left ventricle during systole. That is to say that the arearelating to systole represents the capillary flow rate during systole,while the heart flow rate stored by expansion of the artery duringsystole is represented by the area relating to diastole.

The pressure profile thus provides information immediately on thefraction of systolic ejection which is stored in the artery, and in thevariable volume of the pump if the pump is active, and the fractionwhich is perfused directly into the downstream arterial network (or intothe capillaries, ignoring any expansion of arteries downstream).

I claim:
 1. A circuit (26) for controlling an implantable heart-assistpump (10) of the back-pressure balloon type, which pump comprisesvariable volume means (24) cooperating with a variable volume (20)through which blood flows for the purpose of modifying said variablevolume (20) cyclically and in controlled manner,the circuit beingcharacterized in that it includes (i) heart-assist control means forcontrolling the variable volume means and cooperating with (ii) meansfor sensing data representative of the state of the cardiovascularsystem, said sensing means comprising at least one means selected fromthe group consisting of:means for sensing data representative of aorticpressure (P(t); means for sensing data representative of venous oxygenconcentration (PO_(2V)); means for sensing data representative of aorticoxygen concentration (PO_(2A)); means for sensing data representative ofheartbeat frequency (F); and means for sensing data representative ofthe myocardial contractility (dP/dt).
 2. The circuit of claim 1, whereinthe heart-assist control means includes at least one of the meansselected from the group consisting of:means for controlling the rate ofvariation (u(t)) of said variable volume during systolic phase ofmyocardium; means for controlling the rate of variation (v(t)) of saidvariable volume during diastolic phase of the myocardium; means forcontrolling the instant (t_(A)) at which said variable volume variationstarts during the systolic phase; and means for controlling the instant(t_(R)) at which said variable volume variation starts during thediastolic phase.
 3. The circuit of claim 2, in which operation of theheart-assist control means is predetermined on the basis of a programmedappliance:(i) programmed with a set of rest values for at least onereference parameter selected from the group consisting of: the rate(u(t)) at which the volume varies during the systolic phase of themyocardium; the rate (v(t)) at which the volume varies during thediastolic phase of the myocardium; the instant (t_(A)) at which saidvolume variation during the systolic phase begins; and the instant(t_(R)) at which said volume variation during the diastolic phasebegins; and (ii) programmed with an algorithm for correcting at theleast one reference parameter as a function of the heartbeat frequency(F).
 4. The circuit of claim 2, further including means for sensing data(MV), representative of the metabolic needs of the patient, cooperatingwith said heart-assist control means.
 5. The circuit of claim 4, inwhich operation of the heart-assist control means is automatic on thebasis of:(i) said means for sensing data sensing a representative dataset generated in real time comprising at least sensed parameters of:aortic pressure (P(t)); venous oxygen concentration (PO_(2V)); aorticoxygen concentration (PO_(2A)); heartbeat frequency (F); and myocardialcontractility (dP/dt); (ii) a programmed appliance programmed with a setof reference parameters corresponding to said sensed parameters; (iii)differences determined between said representative data set and saidreference parameters set; and (iv) an algorithm programmed on saidprogrammed device for implementing the variable volume means as afunction of said differences determined; in which the algorithm forimplementing the variable volume means serves to track heart assistance.6. The circuit of claim 5, in which said algorithm serves to track heartassistance by applying the assistance by successive approximations. 7.The circuit of claim 2, further including means for sensing data (G),representative of the physical activity of the patient, cooperating withsaid heart-assist control means.
 8. The circuit of claim 7, in whichoperation of the heart-assist control means is automatic on the basisof:(i) said means for sensing data sensing a representative data setgenerated in real time comprising at least sensed parameters of: aorticpressure (P(t)); venous oxygen concentration (PO_(2V)); aortic oxygenconcentration (PO_(2A) ; heartbeat frequency (F); and myocardialcontractility (dP/dt); (ii) a programmed appliance programmed with a setof reference parameters corresponding to said sensed parameters; (iii)differences determined between said representative data set and saidreference parameters set; and (iv) an algorithm programmed on saidprogrammed device for implementing the variable volume means as afunction of said differences determined; in which the algorithm forimplementing the variable volume means serves to track heart assistance.9. The circuit of claim 8, in which said algorithm serves to track heartassistance by applying the assistance by successive approximations. 10.The circuit of claim 2, in which operation of the heart-assist controlmeans is automatic on the basis of:(i) said means for sensing datasensing a representative data set generated in real time comprising atleast sensed parameters of: aortic pressure (P(t)); venous oxygenconcentration (PO_(2V)); aortic oxygen concentration (PO_(2A));heartbeat frequency (F); and myocardial contractility (dP/dt); (ii) aprogrammed appliance programmed with a set of reference parameterscorresponding to said sensed parameters; (iii) differences determinedbetween said representative data set and said reference parameters set;and (iv) an algorithm programmed on said programmed device forimplementing the variable volume means as a function of said differencesdetermined.
 11. The circuit of claim 10, in which the algorithm forimplementing the variable volume means serves to track heart assistance.12. The circuit of claim 11, in which said algorithm serves to trackheart assistance by applying the assistance by successiveapproximations.